Safari Technology Preview 238 has just dropped for macOS Tahoe and macOS Sequoia, packing a host of improvements that make browsing smoother, safer, and more developer-friendly. Whether you're a web developer testing cutting-edge features or an early adopter who loves staying ahead of the curve, this release brings meaningful changes across animations, CSS, forms, networking, and more. If you already have the preview installed, you can update via System Settings → General → Software Update. Below, we break down the ten most notable updates in this build—each with its own spotlight. Dive in to see what’s new and why it matters.
1. Threaded Animations for Smoother Performance
Animations just got a major speed boost. Safari now uses threaded time-based animation resolution, which means accelerated animations—including CSS Motion Path—run off the main thread. This not only improves performance but also synchronizes them with scroll-driven animations. The result? Buttery‑smooth motion without jank, even on complex pages. Developers working with CSS animations will notice a big difference in responsiveness.
2. The New CSS :open Pseudo‑Class
Web designers now have more control over form elements and other interactive components. The :open pseudo‑class lets you style elements that are in an open state, such as expanded dropdowns or dialogs. This makes it simpler to create consistent, accessible UI without relying on JavaScript to toggle classes. It’s a small addition with big implications for CSS-based interactivity.
3. Smarter CSS Overflow and Gradient Fixes
Two bug fixes clean up rendering quirks. First, the computation for scrollable overflow in block containers now correctly accounts for padding-inline-end, aligning with the CSS Overflow specification. Second, linear gradients with all color stops at the same position now render properly instead of breaking. These changes mean fewer layout surprises and more predictable styling.
4. Chinese Text Conversion for Editing
If you work with multilingual text, this one’s for you. The “Transformations” submenu now includes menu items to convert editable text between Simplified and Traditional Chinese characters. It’s a handy tool for content editors and translators who need quick conversions right inside the browser.
5. Customizable Select Elements
Forms get a big upgrade with the customizable <select> element. Using the new appearance: base-select property, you can style dropdowns with custom content and layouts—no more ugly default popups. This brings native select elements closer to what developers used to achieve only with custom JavaScript widgets, improving both aesthetics and accessibility.
6. Phishing Fix: IDN Homograph Protection
Security gets a boost with a fix that prevents internationalized domain name (IDN) homograph attacks. Safari’s address bar could previously display a lookalike Latin domain as visually identical to a real one, tricking users into phishing sites. Now Safari properly distinguishes these deceptive strings, keeping you safer while browsing.
7. Better URL Encoding for Non‑UTF‑8 Character Sets
Another networking fix addresses incorrect URL query percent‑encoding when using character encodings like iso‑8859‑2, windows‑1250, or gbk. This ensures that special characters in URLs are properly encoded, preventing broken links or data corruption when dealing with legacy encodings. It’s a behind‑the‑scenes improvement that matters for international web apps.
8. Rendering Performance: No More Table Hangs
Tables with a large number of rowspan="0" cells used to cause browser hangs. This release fixes that performance issue, so complex table layouts render smoothly. If you work with data-intensive tables or legacy HTML, this is a welcome stability improvement.
9. SVG Compliance Updates
Three SVG fixes bring Safari closer to spec compliance. The default values for fx and fy on SVGRadialGradientElement now correctly default to 50%. Invalid viewBox values (like negative dimensions) are ignored, matching Firefox and Chrome. And SVG length attributes reset to defaults when removed, rather than retaining old values. These changes make SVG rendering more predictable across browsers.
10. ReadableStream Enhancements
Web API fans get two improvements for streams. Safari now supports ReadableStream.from() to create a stream from async iterables or iterables, simplifying data pipeline code. Additionally, you can transfer ReadableStream objects via postMessage(), enabling efficient sharing of streaming data between contexts like workers or iframes. Both features open up new possibilities for real‑time data processing.
These ten updates make Safari Technology Preview 238 a formidable release for developers and power users alike. From performance boosts under the hood to polished UI features, each change contributes to a faster, safer, and more capable browsing experience. If you haven’t tried the preview yet, now is a great time to explore what’s coming next in Safari.